diff --git a/src/vim9compile.c b/src/vim9compile.c
index e4656c9..c5a2c2d 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -1240,13 +1240,16 @@
 
 /*
  * Generate an ISN_GETITEM instruction with "index".
+ * "with_op" is TRUE for "+=" and other operators, the stack has the current
+ * value below the list with values.
  */
     static int
-generate_GETITEM(cctx_T *cctx, int index)
+generate_GETITEM(cctx_T *cctx, int index, int with_op)
 {
     isn_T	*isn;
     garray_T	*stack = &cctx->ctx_type_stack;
-    type_T	*type = ((type_T **)stack->ga_data)[stack->ga_len - 1];
+    type_T	*type = ((type_T **)stack->ga_data)[stack->ga_len
+							  - (with_op ? 2 : 1)];
     type_T	*item_type = &t_any;
 
     RETURN_OK_IF_SKIP(cctx);
@@ -1260,7 +1263,8 @@
     item_type = type->tt_member;
     if ((isn = generate_instr(cctx, ISN_GETITEM)) == NULL)
 	return FAIL;
-    isn->isn_arg.number = index;
+    isn->isn_arg.getitem.gi_index = index;
+    isn->isn_arg.getitem.gi_with_op = with_op;
 
     // add the item type to the type stack
     if (ga_grow(stack, 1) == FAIL)
@@ -6746,19 +6750,17 @@
 		int	is_const = FALSE;
 		char_u	*wp;
 
+		// for "+=", "*=", "..=" etc. first load the current value
+		if (*op != '='
+			&& compile_load_lhs_with_index(&lhs, var_start,
+								 cctx) == FAIL)
+		    goto theend;
+
 		// For "var = expr" evaluate the expression.
 		if (var_count == 0)
 		{
 		    int	r;
 
-		    // for "+=", "*=", "..=" etc. first load the current value
-		    if (*op != '=')
-		    {
-			if (compile_load_lhs_with_index(&lhs, var_start,
-								 cctx) == FAIL)
-			    goto theend;
-		    }
-
 		    // Compile the expression.
 		    instr_count = instr->ga_len;
 		    if (incdec)
@@ -6795,7 +6797,7 @@
 		{
 		    // For "[var, var] = expr" get the "var_idx" item from the
 		    // list.
-		    if (generate_GETITEM(cctx, var_idx) == FAIL)
+		    if (generate_GETITEM(cctx, var_idx, *op != '=') == FAIL)
 			goto theend;
 		}